Update to python-telegram-bot v20

Version 2.0

It was updated to python-telegram-bot v20.

Other changes:

• Uses a Constants.py file to store tokens and sensible information instead of plain text.
• Doesn't download and remove images anymore.
• Uses Telegram Jobs to execute the image sending to the targeted chat (in this case @AstropixChannel) as a daily task.
• Includes polling so you can interact with the bot while testing it.

First release - Stable version of the bot

Version v1.0

Basic implementation.

Sends the picture of the day to a targeted chat (in this case to @AstropixChannel) and, in case of a video, sends de YouTube thumbnail.